Unable to boot Windows 7 (dual boot)

I have a dual boot system with Windows 7 (office) and Windows 10 (games). These are installed to 2 separate SSDs. There is also a third shared data drive. This has all worked fine for a number of years with the Windows Bootloader menu.

I was tinkering with the CSM in the BIOS last week to try and resolve an unrelated issue when I found I was unable to POST the machine. I did succeed in recovering the BIOS, and the settings are now back to default with CSM enabled. I was subsequently able to boot into Windows 10, but I am no longer able to boot Windows 7.

Windows repair tool gives an error of "boot configuration file corrupted". I have a working entry in the boot menu, and I see the Windows logo appear but that is all. In safe mode it loads some drivers and fails. I can see all the data on the disk from the other OS and the disk does not register any errors.

I have worked through the options in Easy BCD. Resetting the BCD configuration made the PC unbootable but I was able to recover this by allocating drive letters to the necessary volumes and manually rebuilding via the command prompt (using an installation disc).

I am guessing I am now at the end of this journey and need to reinstall 7. How will I need to set things up to be able to boot into Windows 10 ? Both disks are GPT. The EFI system partiton is on the 1st drive with Windows 7.

I've had my share of dual boot dramas over the years but this EFI has stumped me. Any help gratefully received!


Knows where his towel is.
Staff member
Can you post the contents of EasyBCD "view settings" (detailed mode) and a screenshot of your Disk Management.


Knows where his towel is.
Staff member
Terry, thanks for taking the time to review this.

The problem was in the UEFI defaults.

I changed the SATA setting from IDE to AHCI which allowed Windows 7 to boot (hurrah!).

This however knocked out Windows 10.

The final fix was to configure Windows 10 to start in safe mode (once) using the Advanced tab of Advanced Settings in Easy BCD.

This reset the storage drivers and everything is now fine and back to how it was.

Not entirely sure how this state of affairs came about but Easy BCD was a great help in sorting it out, many thanks.